The design of a proton or ion radiation therapy system for a clinical environment should take account of overall size, cost, and complexity. Available space is usually limited in crowded clinical environments. Lower cost allows more systems to be deployed to reach a broader patient population. Less complexity reduces operating costs and makes the system more reliable for routine clinical use.
Other considerations may also bear on the design of such a therapy system. By configuring the system to apply the treatment to patients who are held in a stable, reproducible position (for example, lying supine on a flat table), the physician can more precisely relocate the intended target, relative to the patient's anatomy, at each treatment. Reliable reproduction of the patient's position for each treatment also can be aided using custom molds and braces fitted to the patient. With a patient in a stable, fixed position, the radiotherapy beam can be directed into the patient from a succession of angles, so that, over the course of the treatment, the radiation dose at the target is enhanced while the extraneous radiation dose is spread over non-target tissues.
Traditionally, an isocentric gantry is rotated around the supine patient to direct the radiation beam along successive paths that lie at a range of angles in a common vertical plane toward a single point (called an isocenter) within the patient. By rotating the table on which the patient lies around a vertical axis, the beam can be directed into the patient along different paths. Other techniques have been used to vary the position of the radiation source around the patient, including robotic manipulation.